Photoreceptor cleaning device for electrophotographic copying apparatus of the dry cleaning agent type

ABSTRACT

A device adapted for use with electrophotographic copying apparatus of the dry cleaning agent type which performs one cycle of copying operation while its photoreceptor makes two revolutions, with charging, exposing, developing and transfer printing being carried out during a first revolution and cleaning of the photoreceptor being carried out during a second revolution. A magnetic brush used for developing during the first revolution is diverted for removing residual toner particles from the photoreceptor during the second revolution and cooperates with a cleaning blade so as to clean the photoreceptor and recover the residual toner particles from the photoreceptor to the developing agent container.

United States Patent [191 Narita Nov. 11, 1975 [75] Inventor: Teruo Narita, Tokyo. Japan {73] Assignee: Ricoh Co., Ltd., Tokyo, Japan [22] Filed: Dec. 3, 1973 [21] Appl. No.: 421,435

[30] Foreign Application Priority Data Dec. 21. 1972 Japan 47-128932 Apr. 18. 1973 Japan 4846103 [52] U.S. Cl. 355/15; 15/1.5; 15/25651;

[51] Int. Cl. G03G 21/00 [58] Field of Search 355/15. 3 DD; 117/175;

[56] References Cited UNITED STATES PATENTS 3.552.850 1/1971 Royka et al 355/15 3.660.863 5/1972 Gerbasi 355/15 3.685.485 8/1972 Kutsuwada et al.. 355/3 DD 3.700.328 10/1972 Davidge et al. 355/3 DD 3,728,016 4/1973 Harbour et al. 355/15 3.742.551 7/1973 Oriel 355/15 5/1971 Gerbasi 355/15 3.752.576 3.793.986 2/1974 Latone 355/15 3.8l9,26l 6/1974 Ogawa 355/14 OTHER PUBLICATIONS Toner Reclaiming System," F. W. Johnson et al., IBM Technical Disclosure Bull, Vol. 14, No. 1. June7l. pp. 235.

Primary E.\'aminerRichard L. Moses Attorney, Agent. or Firm--Cooper. Dunham, Clark. Griffin & Moran 5 7 ABSTRACT A device adapted for use with electrophotographic copying apparatus of the dry cleaning agent type which performs one cycle of copying operation while its photoreceptor makes two revolutions. with charging, exposing. developing and transfer printing being carried out during a first revolution and cleaning of the photoreceptor being carried out during a second revolution. A magnetic brush used for developing during the first revolution is diverted for removing residual toner particles from the photoreceptor during the second revolution and cooperates with a cleaning blade so as to clean the photoreceptor and recover the residual toner particles from the photoreceptor to the developing agent container.

5. Claims, 4 Drawing Figures U.S. Patent Nov. 11, 1975 Sheet1of2 3,918,808

U.S. Patent N0v.11,1975 Sheet2of2 3,918,808

FIGB

FIG.4

BACKGROUND. or, THE lNVENTlON This invention relates to a. photoreceptor cleaning devices, and more particularly it is concerned-with photoreceptor cleaning device for electrophotographic copying apparatus of the dry cleaning agent type which performs one cycle of copying operation while its photoreceptor makes two revolutions, with charging, exposingdeveloping and transfer printing being carried out during a first revolution and cleaning of the photoreceptor being carried out during a second revolution. In one type of electrophotoele'ctri'c'copying apparatus known in the art'u'sing as a photoreceptor a photosensitive drum or aph'otosensitive belt wound about the periphery of a drum, a charging device, developing device, t r'ansfer p'rintin'g d'evicefehar'ge removing'deyic'e, cleaning device, and ifatigue relieving device are arranged a'roiiri'd the photoreceptor whereby ohe'cyicle of copying operation charging, exposing, developingftrans ferg charge removing,f'cleaning and fatigue relieviiigcan'be prfornied while'the 'photoreceptor makes 'lcomplete revolution. I i,

i The cleaning station of the aforementioned type of electropho'to'graphic copying appaifatus isnotdisposed adjacentits developing station, This has made it necessary toput aside in some other poisition thede veloping agent which has been recovered by cleaning the photoreceptor. More specifically, the cleaning station is disposed anterior. to the transfer-printing station in the direction of rotation of the photosensitive drum. One:

type of cleaning device comprises a blade and a recoveryroller disposed, below the blade. The blade is used forcleaning the surface of the photoreceptor while the roller is maintainedinengagement with or spaced apart from the surface of the photoreceptora small distance and rotated at least during the time the blade is performing a cleaning operation or the photoreceptor is rotating, so that the developing agent removed by the cleaningoperationfrom the photoreceptor is moved to the surface of the roller. Another-,type of cleaning de-' vice comprises. aycleaning-agent which isused for wiping the .phqtoreceptortoathcreby remove the develop- The former type-requircs -alargef container for storing therein thetoner particles of the developing agent removed from the photoreceptor. The tonerparticles recovered in this way have to be returned, either manually'or -by using an automatic conveyor means to the developing station. w I

- In addition, cleaning devicesof the prior art have the disadvantage of the recovered tonerparticlesscattering and "soiling the adjacent parts when recovered. As aforementioned, somemean is required to return the recovered toner particle'st'o the developing station-because the developing station is'r'erno te' from the clean-v ingistat'ion'. it wouldthus be po' 'sisible" to obviate the aforementioned"disadvantages of the' prior' art if the cleaning station w'ere disposed adjaceiit-the' developing station so that the recovered toner can be directly returned to the developing station.

Thisarrangcmcnt is not possiblc.'howcver. in a copying apparatus wherein one cycle of copying operation is performed while the photoreceptor makes one revolution. If the developing station were disposed adjacent the cleaning station in such apparatus, an electrostatic latent image formed by exposing the photoreceptor to an. optical image of an original or a tonerimage formed by developing the latent image into a visible image would'be'wiped' away andno duplicate ofthe original could be produced. v

In order to obviate the disadvantages of the priorzart,

. it is proposed in the present invention to make the photoreceptor rotate twice while one cycle of operation is performed, with charging, exposing, developing and transfer printing being carried out during a first revolu- .tion and cleaning of the photoreceptor beingcarried out during a second ICVOlUtiOIlz If the electrophotographic apparatus could be made to operate-as aforementioned, it would be possible to arrange thecleening station to be disposed adjacent the developin g station. 5 "On the otherhand, in case a well-known magnetic brush is used as a means for developing a latent image with a dry developing agent, a magnetic brush formed on a magnetic drum by a dry .developing agent: at-

tracted thereto supplies the dry developing agent to the photoreceptor when there is an electrostatic latent image formed thereon but merely slides along the surface of the photoreceptor whenino electrostaticlatent image is formed thereon. Thus,the surfaceofthe photoreceptor is wiped clean by the brush.

' SUMMARY OF THE INVENTION- This invention has 5; its object the provision of a photoreceptor vcleaning device for electrophotographic copying apparatus of the-dry cleaning agent type using a magnetic brush for developingwhich performs one cycle of copying operation while its photoreceptor makes two-revolutions, with charging, exposing, developing and transfer printing being carried out during a first revolution and cleaning of the photoreceptor being carried out during a second revolution, such cleaning device comprising a--.blade disposed in .the vicinity of the magnetic brush and adapted to clean the surface of the photoreceptor by removing the residual developing agent therefrom andautomatically returning the same to the developing device, themagnetic brush beingeffective to slide along the surface of the photoreceptor I after the'operation of theblade is completed so as to remove therefrom any developing agent which, might otherwise remain'thereon. I

The outstanding characteristic ofthe invention is that the cleaning device is disposed within or in the vicinity of the developing device of an electrophotographic copying apparatus comprising a photoreceptor adapted to make 2 revolutions while one cycle ofcopying oper- "ati onis performed. This offers many advantages. The

toner particles removed from the surface of the photoreceptor bythe cleaning device can be automatically returned tothe developing device for reuse. The provision of the cleaning device in the vicinity of the develparticles recovered from the photoreceptor by cleanings l'his makes it possible to obtain an overall compact -size in an electrophotographiccopying apparatus, to

simplify the construction of such apparatus and to reduce its cost.

An additional feature of the invention is that the magnetic brush used for developing is divered for use as a cleaning agent when cleaning of the photoreceptor is performed, thereby enabling to remove from the photoreceptor any toner particles which might otherwise remain thereon after cleaning is carried out by the blade. Since the blade is disposed above the magnetic brush, any toner which may drop from the blade is deposited on the magnetic brush, thereby preventing scattering of toner particles and soiling of the adjacent parts by the dropping toner particles.

Preferably, the cleaning blade is made of a material of low electric insulation, so that the residual charge on the photoreceptor can be made to escape through the cleaning blade when the latter is brought into contact with theformer, thereby permitting the residual charge on thephotoreceptor to be lowered to facilitate cleaning .of the photoreceptor.

I BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an electrophotographic copying apparatus in which one embodiment of this invention is incorporated;

- FIG. 2 is a side view showing means for bringing the .cleaning blade-into and out of engagement with the DESCRIPTION OF THE PREFERRED EMBODIMENTS Before'describing the invention, an electrophotographic copying apparatus of the dry developing agent type in which the invention can be incorporated'will 1 first be outlined. In FIG. 1, there is shown a photoreceptor in the form of a photosensitive drum I mounted on a shaft 2 driven by a drive source (not shown) to rotatethe photosensitive drum 1 in the direction. of an arrow at a predetermined rate. One cycle of copying operation is performed while the photosensitive drum 1 makes two revolutions, with charging, exposing, de-

;veloping and transfer printing being carried out during afirst rotation and cleaning of the photosensitive drum being carried out during a second revolution. Disposed around the periphery of the photosensitive drum 1 is a charging device 3, exposing device 4, cleaning blade 5, developing device of the magnetic brush type 6, transfer-printing device 7, sheet stripping device 8, charge removing device 9 and fatigue relieving device 10 arranged in the direction of rotation of the photosensitive drum 1 in the indicated order. The charging device 3, exposing device 4, developing device 6, transferprinting device 7, sheet stripping devices, charge removing device 9 and fatigue relieving device 10 all cooperate with the photosensitive drum to perform an electrophotographic copying operation during the first revolution of the drum while the cleaning blade 5 performs cleaning of the surface of the drum during its second revolution with the magnetic brush of the developing device 6 acting as a cleaning agent when cleaning is carried out. The process of electrophotographic copying will no be described. As the photosensitive drum 1 rotates, the

entire surface of the drum is uniformly charged by the charging device 3. Then the charged surface of the photosensitive drum 1 is exposed to an optical image of an original to be duplicated by the exposing device 4 which is of the original moving type and slit exposure system in this embodiment. Alternatively, an exposing device of the optical system moving type and slitexposure system may be employed. The exposing device of the type shown comprises, as is well known, a transparent original support member 11 moving in the direction, of an arrow b in synchronism with the movement of photosensitive drum 1, a light source 12 for illuminating the original resting on the original support member 11, and a slit 19 formed by a reflector IS, lens 14, reflectors l5, l6, l7 and diaphragm members 18a, 18b through which the light from the original is incident on the charged surface of the photosensitive drum 1 to expose the same to an optical image of the original. Al electrostatic latentimage of the original is formed on the surface of the photosensitive drum 1 in this way.

The electrostatic latent image is developed with a dry developing agent by the developing device 6 as the photosensitive drum 1 further rotates. The developing device 6, which is of the magnetic brush type as aforementioned, comprises a non-magnetic sleeve 20 having built therein a magnet (now shown) and driven to roparticles in the developing agent 22. The developing agent remaining on the non-magnetic sleeve 20 is scraped off the sleeve 20 into the container 21 by a scraping plate 23. I

The visible toner image formed on the photosensitive drum 1 is printed on a transfer-printing copy sheet 24 "bythe transfer-printing device 7. Such copy sheet 24 is one of a number of sheets cut beforehand from astrip or web in a predetermined size and stored in a cassette one on another. Astack of copy sheets is piledon a sheet feed tray 25, and the uppermost sheet is delivered by a sheet feed roller 26 to a guide plate 27, from which it is delivered by a pair of conveyor rollers 28a, 28b to a guide plate 29, from which it is further delivered by a pair of conveyor rollers 30a, 30b and guide plates 31a, 3 lb to a portion of the surface of the photosensitive drum 1 on which the visible toner image is formed. The visible toner image-is printed on the copy sheet 4 by the transfer printing device 7.

The two pairs of conveyor rollers 28a, 28b and 30a, 30b of the sheet feed mechanism rotate in synchronism with the rotation of the photosensitive drum 1, while the sheet feed roller 26 of the mechanism is adapted to make a complete revolution at regular intervals so as to deliver the uppermost sheet from the pile of sheets 24. The copy sheet fed by the sheet feed roller 26 is adapted to have its leading end nipped by the pair of conveyor rollers 28a, 28b, and the sheet 24 nipped by the conveyor rollers 28a, 28b is pulled out of the pile of sheets as the rollers 28a, 28b rotate. Thus, when the sheet feed roller 26 completes its one revolution, it rotates as the sheet is pulled out by the rollers'28a, 28b.

The copy sheet 24 on which the visible toner image photosensitive drum 1 is stripped from the photosensitivc drum by pick-off claw means 8 and delivered by a veloping is diverted for use as a cleaning magnetic conveyor means 32 to a fixing device 33. where the toner image is fixed to the copy sheet 24 and discharged from the apparatus to outside by a pair of discharge rollers 34a, 34b. On the other hand, the electric charge on the surface of the photosensitive druml is removed by the charge removing device 9, and then the photosensitive drum 1 is relieved of fatigue by the fatigue relieving device 10. Thus, as the photosensitive drum 1 makes one complete revolution, one duplicate of the original is produced.

As can be clearly understood from the description of the electrophotographic apparatus set forth above, the toner particles in the developing agent 22 in the container 21 of the developing device grow smaller in quantity as each copy sheet is printed. The developing agent 22 used in the developing device 6 of the dry developing agent type consists of toner particles for forming a visible image, and a carrier adapted to supply the toner particles to the electrostatic latent image on the photosensitive drum. The carrier is adapted to be attracted by the magnet in the non-magnetic sleeve to form a magnetic toner brush on the surface of the sleeve 20 so as to deliver the toner particles to the electrostatic latent image. The carrier is scraped off the surface of the sleeve 20 and returned to the container 21 after the toner particles are supplied to the drum 1. Thus, it is the toner particles alone which'grow smaller in quantity as the copying operation is repeated.

An additional supply of toner particles is delivered through a hopper 35 disposed above the developing agent container 21. In addition to the hopper 35, the toner supply device comprises a toner supply roller 36 disposed in an outlet port 35a formed at the bottom of the hopper 35. The roller 36 is rotated at a suitable time to deliver a fresh supply of toner through the outlet port 35a into the container 21. The toner particles delivered to the container2l in this way are agitated by agitating blades 38 in the container 21 and mixed with the carrier.

After developing is completed, the developing agent remaining on the sleeve 20 is scraped off the sleeve by the scraping plate 23 and returned to the container 21 while being agitated by an agitator 39 on the scraping plate.

In FIG. 1, 40 designates a fan for cooling the interior of the copying apparatus, 41 a drive source, and 42 an electric equipment.

One form of the copying apparatus in which the invention can be incorporated is constructed as aforementioned. A duplicate of an original is produced while the photosensitive drum 1 makes one complete revolution, and the surface of the photosensitive drum 1 is cleaned by cleaning device according to the invention while the drum 1 makes another complete revolution.

The cleaning device according to the invention will now be described in detail. As shown in FIG. 2, the cleaning device comprises a cleaning blade 5 made of a resilient material having a forward end portion 5a maintained in light engagement with a portion of the surface of the photosensitive drum 1 which is disposed above a portion of the surface of the photosensitive drum 1 with which the magnetic brush 43 is brought into engagement, and a cleaning magnetic brush for removing from the drum surface the toner particles still remaining thereon after cleaning is performed by the cleaning blade 5. The magnetic brush 43 used for debrush. Thus, the magnetic brush 43 acts as a developing magnetic brush when there is an electrostatic latent image on the surface of the photosensitive drum I or during the first revolution of the drum 1, and as a cleaning magnetic brush when there is noelectrostatic latent image on the surface of the drum 1 or during the second revolution thereof.

The cleaning blade 5 disposed immediately above a portion of the magnetic brush 43 which is brought into contact with the surface of the drum 1 is made of a resilient material, eg rubber or polyurethane foam, which does not damage the drum surface and in the form of a bar extending along the support shaft 2. The blade 5 has a-base portion Sb at one end disposed opposite to the forward end portion 5a lengthwise thereof and positionedagainst the periphery of a shaft 44 disposed parallel to the support shaft 2 for the drum 1. The base portion 5b is wrapped by a resilient plate 45 wound on the shaft 45, so that the blade 5 is supported by the shaft 44 and acts as a unit therewith. The forward end portion 5a of the cleaning blade 5 is maintained in engagement with the portion of the surface of the drum 1 which is disposed above the portion of the drum 1 with which the magnetic brush 43 is brought into engagement with the surface of the drum 1 as aforementioned. The shaft 44 is rotatably supported at opposite ends thereof by side walls (not shown) of the developing agent container 31 (see FIG. 1), and extends out of the apparatus at one end portion. Thus, by turning the one end portion of the shaft 44 extending out of the apparatus, it is possible to bring the cleaning blade 5 forward end portion 5a into and out of engagement with the surface of the drum 1.

The range of rotation of the shaft 44 is limited by a segmental stopper 46 affixed at its base to the shaft 44 and having affixed to its free end portion a pin 47. A loop spring 49 tending to expand is mounted between the pin 47 and a pin 48 affixed to one of the side walls of the developing agent container 21 (See FIG. 1 The loop spring 49 operates such that when the pin 47 moves rightwardly (in FIG. 2) of the imaginary line connecting the pin 48 with the shaft 44 it causes by its resilience the:stopper 46 to move in pivotal movement clockwise aboutthe center axis of the shaft 44 to a predetermined position shown in FIG. 3, and that when the pin 47 moves leftwardly (in FIG. 3) of the imaginary lineit causes by its resilience the stopper plate 46 to move in pivotal movement counter clockwise about the center axis of the shaft 44 back to its position shown in FIG. 2. The positions in which the stopper 46 stops when moving clockwise and counter clockwise about the shaft 44 are fixed by a window 50 formed in one of the side walls of the developing agent container 21. The window 50 receives therein a bent portion 46a formed at one edge of the stopper 46, so that the range of pivotal movement of the stopper 46 is limited by the range of pivotal movement of the bent portion 46a in the win- Idow 50.

One of the reasons why the cleaning blade 5 is detachably mounted on the shaft 44 relative to the photosensitive drum 1 is because the photosensitive drum 1 "of the copying apparatus in which the invention is inobstruct the movement of the drum 1 into and out of the apparatus. Another reason is that. since the forward end portion 5a of the cleaning blade 5 is preferably maintained in engagement with the surface ofthe drum 1 with a light force. the arrangement in which the cleaning blade 5 is detachably supported by the shaft 44 in cooperation with the stopper 46 and loop spring 49 serves this purpose. i The stopper 46 has affixed thereto a shaft 51 which in turnhas affixed thereto a member 52 of small thickness made of Mylar or other synthetic resinous material. The member 52 of small thickness is intended to keep the toner particles scraped off the drum surface by the cleaning blade 5 from scattering in all directions and moving upwardly. t

.The cleaning device according to the invention constructed as aforementioned operates as follows. As the photosensitive drum 1 makes its second revolution, the residual toner particles on the surface of the drum 1 are removed by the forward end portion 5a of the cleaning blade 5. At this time, the charge carried by the surface of the drum 1 has already been removed by the charge removing device 9 and the toner particles do not adhere to the surface of the drum 1, so that they merely float on the drum surface. Thus, no resistance is-offered to the cleaning blade by the residual toner particles when the former is operated to remove the latter. The removed toner particles drop on to the sleeve or directly .into the developing agent container 21.

#:The residual toner particles which still remain on the surface of the drum 1 after the cleaning blade 5 is operated are removed by the cleaning magnetic brush 43 which slides along the drum surface as the photosensitive drum 1 rotates. In this way, the surface of the photosensitive drum 1 is cleaned and ready for the next copying operation when the drum hascompleted two revolutions.

In the embodiment shown and described above, the cleaning blade is disposed above the magnetic brush 43. Alternatively, a blade 105 may be disposed below the magnetic brush 43 as shown in FIG. 4. When the blade 105 is disposed below the magnetic brush 43 as shown, the blade 105 must be brought out of engagement with the surface of a drum 11 when the latter makes its first revolution. If the blade 105 were maintained in engagement with the surface of the drum 1], a toner image formed on the surface of the drum 11 in the first revolution of the drum would be destroyed. In the embodiment shown, the blade 105 pivotally sup- .ported by a shaft 144 is adapted to be brought into engagement with the drum surface when a cleaning operation is performed and out of engagement therewith when no cleaning operation is performed by the action of a solenoid or the like. The embodiment constructed as aforementioned can achieve the same results as the embodiment shown in FIG. 2 and FIG. 3. The embodiment shown in FIG.'4 requires no toner scattering preventing member. In this embodiment, a sleeve 120 mounted in a developing agent container 121 to which a fresh supply of toner particles 137 is delivered through a hopper 135 rotates in an opposite direction to the rotation of the counterpart of the embodiment shown in FIG. 2. Accordingly, a scraper 123 is disposed in a position opposite to that of the counterpart of the embodiment'shown in FIG. 2.

Preferably; the blade 105 is made of a material low in electric insulation, so that the residual charge on the photosensitive drum II can be made to escape through the cleaning blade to lower the level of residual charge while scraping the residual toner particles off the drum. On the other hand, since the blade 5 of the embodiment shown in FIG. 2 is maintained in pressing engagement with the photosensitive drum 1 at all times, the blade 5 is preferably electrically insulating to a degree such that no deleterious influences are exerted on the electrostatic latent image formed on the photosensitive drum. The results of experiments show that the specific resistance of the blade 5 is over 10 0. cm. If this value is suitably reduced, it is possible to eliminate the occurrence of background density in a copy sheet because the surface potential of non-image portions of the pho tosensitive drum 1 is reduced, althoughit has deleterious effects on the electrostatic latent image to a certain extent.

The photosensitive drum can also be cleaned by impressing on the drum a bias voltage of the nature such that the residual toner particles are removed therefrom.

It is to be understood that a photosensitive belt may be used and wound on the periphery of a drum in place of using a photosensitive drum.

What is claimed is:

1. In electrophotographic copying apparatus of the dry toner image transfer type, in combination,

a. a photoreceptor unidirectionally movable along a closed endless path and undergoing two complete revolutions around said path during each cycle of copying operation; and a b. means, disposed in succession along said path so as to be traversed successively by said photoreceptor during each complete revolution thereof around said path, for erasing charge from saidphotoreceptor, charging said photoreceptor, exposing said photoreceptor in charged condition to form an electrostatic latent image thereon, developing the electrostatic latent image on said photoreceptor, and transfer printing the developed image;

wherein the improvement comprises: 7

c. said charging, exposing, and transfer printing means comprising means for charging said photoreceptor, forming a latent image thereon and transfer printing a developed image only once in each cycle of copying operation, during only the first of the two successive revolutions of said photoreceptor around said path constituting said cycle, and being inoperative during the second of said two successive revolutions constituting said cycle;

d. said erasing means comprising means for erasing charge from said photoreceptor at least during the second of said two successive revolutions of said photoreceptor such that said photoreceptor traverses said developing means in charged condition during. said first revolution and in charge-erased condition during said second revolution in each cycle of copying operation; and

e. said developing means comprising a magnetic brush for transferring dry toner particles to said photoreceptor to develop an electrostatic latent 7 image thereon when said photoreceptor traverses the developing means in charged condition and for removing residual toner particles from said photo receptor to clean said photoreceptor when said photoreceptor traverses the developing means in charge-erased condition, such that said magnetic brush develops an image on the photoreceptor during the first. and cleans the photoreceptor during the second. ofthe two successive revolutions of the photoreceptor constituting one cycle of copying operation.

2. Apparatus as defined in claim 1 further comprising a blade means disposed anterior to said magnetic brush and having its forward end portion brought into pressing engagement with the surface of the photoreceptor at least during the second revolution for aiding the cleaning by the magnetic brush.

3. Apparatus as defined in claim 2 wherein said blade means is comprised of a material having some electrical conductivity for removing residual potential from the photoreceptor when in pressing engagement therewith.

4. Apparatus as defined in claim 1 further comprising a blade means disposed posterior to the magnetic brush. and having its forward end portion brought out of engagement with the surface of the photoreceptor during the first revolution and into pressing engagement therewith during the second revolution. for finishing the cleaning by the magnetic brush.

5. Apparatus as defined in claim 1, further including a. means for holding a supply of developing agent including dry toner particles in position for pickup of the developing agent by the magnetic brush; and

b. a blade disposed adjacent said magnetic brush for contact with the photoreceptor to scrape toner particles from the surface thereof;

c. said holding means being so positioned that toner particles scraped from the photoreceptor by said blade fall into said holding means in position for pickup by said magnetic brush. 

1. In electrophotographic copying apparatus of the dry toner image transfer type, in combination, a. a photoreceptor unidirectionally movable along a closed endless path and undergoing two complete revolutions around said path during each cycle of copying operation; and b. means, disposed in succession along said path so as to be traversed successively by said photoreceptor during each complete revolution thereof around said path, for erasing charge from said photoreceptor, charging said photoreceptor, exposing said photoreceptor in charged condition to form an electrostatic latent image thereon, developing the electrostatic latent image on said photoreceptor, and transfer printing the developed image; wherein the improvement comprises: c. said charging, exposing, and transfer printing means comprising means for charging said photoreceptor, forming a latent image thereon and transfer printing a developed image only once in each cycle of copYing operation, during only the first of the two successive revolutions of said photoreceptor around said path constituting said cycle, and being inoperative during the second of said two successive revolutions constituting said cycle; d. said erasing means comprising means for erasing charge from said photoreceptor at least during the second of said two successive revolutions of said photoreceptor such that said photoreceptor traverses said developing means in charged condition during said first revolution and in charge-erased condition during said second revolution in each cycle of copying operation; and e. said developing means comprising a magnetic brush for transferring dry toner particles to said photoreceptor to develop an electrostatic latent image thereon when said photoreceptor traverses the developing means in charged condition and for removing residual toner particles from said photoreceptor to clean said photoreceptor when said photoreceptor traverses the developing means in charge-erased condition, such that said magnetic brush develops an image on the photoreceptor during the first, and cleans the photoreceptor during the second, of the two successive revolutions of the photoreceptor constituting one cycle of copying operation.
 2. Apparatus as defined in claim 1 further comprising a blade means disposed anterior to said magnetic brush and having its forward end portion brought into pressing engagement with the surface of the photoreceptor at least during the second revolution for aiding the cleaning by the magnetic brush.
 3. Apparatus as defined in claim 2 wherein said blade means is comprised of a material having some electrical conductivity for removing residual potential from the photoreceptor when in pressing engagement therewith.
 4. Apparatus as defined in claim 1 further comprising a blade means disposed posterior to the magnetic brush, and having its forward end portion brought out of engagement with the surface of the photoreceptor during the first revolution and into pressing engagement therewith during the second revolution, for finishing the cleaning by the magnetic brush.
 5. Apparatus as defined in claim 1, further including a. means for holding a supply of developing agent including dry toner particles in position for pickup of the developing agent by the magnetic brush; and b. a blade disposed adjacent said magnetic brush for contact with the photoreceptor to scrape toner particles from the surface thereof; c. said holding means being so positioned that toner particles scraped from the photoreceptor by said blade fall into said holding means in position for pickup by said magnetic brush. 